The overall objective of the present study was to investigate the mechanism(s) by which gonadotropins regulate the ovarian function. Investigations were made into the receptor mediated activation of adenylate cyclase to increase the intracellular cAMP level, in situ activation of protein kinase, relationship between receptor saturation and cyclic AMP and progesterone accumulation, the role of lipids in receptor activity and the role of cAMP on RNA synthesis. The following conclusions were made from these studies: 1) Treatment of plasma membranes with phospholipase A and phospholipase C resulted in a loss of gonadotropin binding to the receptor; the phospholipase A mediated inhibition was due to lysophosphatides, whereas the inhibition by phospholipase C was due to loss of the phospholipids that maintain the conformation of receptor; 2) There is a disparity between the receptor occupancy and the intracellular responses such as cyclic AMP accumulation and progesterone synthesis suggesting the existence of spare receptors for LH and HCG in the ovary; 3) The exposure of rat ovarian cells to HCG and LH resulted in the in situ activation of protein kinase and this activation correlated with progesterone synthesis; and 4) Cyclic AMP stimulated RNA synthesis in the ovarian cells in vitro.